Sockets for electrically interconnecting a circuit board daughtercard to a circuit board mothercard are well-known. Such sockets include an insulative housing having an elongated slot for receiving an edge portion of the daughtercard. Contacts in the housing extend into the slot for engagement with contact pads on the daughtercard, and the contacts have leads which extend to an exterior of the housing for engagement with mating circuit traces on the mothercard.
The sockets may be either of the cam-in or direct insertion type. The cam-in type allows the daughtercard to be inserted into the slot at a first orientation with a zero insertion force. The card is then pivoted to a second orientation against spring forces exhibited by the contacts, and the card is retained in the second orientation by a latching device.
In the direct insertion type of socket, the daughtercard is inserted into the slot with a single straight line motion. There may be considerable resistance to insertion of the card due to friction forces of the contacts wiping against the card as the card is inserted into the slot. The contacts exert a normal force on the card in the slot, and these normal forces generate a frictional resistance to removal of the card from the socket. The frictional resistance contributes greatly to retaining the card in the socket and may be sufficient to retain the card in some cases. However, the cards are manufactured with a tolerance on their thickness, and a card that is near the minimum thickness will experience less frictional resistance than a card that is near the maximum thickness. Since vibration, shock and thermal stresses can cause a card to back out of its socket, additional retention mechanisms have been employed to ensure retention of the card therein.
U.S. Pat. No. 4,973,270 discloses a direct insertion type socket having card guides at each end which define grooves aligned with the card receiving slots. Opposed walls of each groove include a pair of opposed ridges which are spaced apart by a distance which is less than a minimum thickness of the card to be received therein. One of the walls is relatively thin so as to be somewhat flexible, thereby permitting the groove to be expanded upon insertion of a daughtercard to accommodate different thicknesses thereof. The ridges on the grooves provide an additional friction force which acts to retain the daughtercard in the socket. Still, the daughtercard is not held in the socket by a positive lock, and the daughtercard may shift in position, experience electrical decoupling, and become loose due to vibration, shock and thermal stresses.
U.S. Pat. No. 4,781,612 discloses a direct insertion socket having a positive lock in the form of a latch. The latch comprises a resilient arm extending from the socket body upwardly to a boss which is normally disposed in an area to be occupied by the card when the card is inserted into the socket. Insertion of the card resiliently deflects the arm until the boss becomes aligned with a hole in the card when the card is fully inserted. The resilient arm then springs back, engaging the boss in the hole and positively retaining the card in the socket. A problem with this locking device is that a tool must be used to push the boss out of the hole or to otherwise deflect the arm in order to remove the card from the socket. Modern electronic packages have components mounted in close proximity such that application of a tool may be difficult. Further, even after the boss is dislodged from the hole the card is still retained by frictional resistance of the contacts, and additional force must be applied to the card to extract the card from the socket.
There is a need for a socket having a positive locking mechanism which is simple and easy to use and does not require application of a tool. There is a further need for a socket having a positive locking mechanism combined with a card extractor mechanism.